Use this rule when choosing whole-grain foods: for every 10 grams of carbohydrate there should be at least one gram of fiber. Why 10:1? That’s about the ratio of fiber to carbohydrate in a genuine whole grain—unprocessed wheat. This recommendation comes from a new report from the Harvard School of Public Health published online in the journal Public Health Nutrition.

Current standards for classifying foods as “whole grain” are inconsistent and, in some cases, misleading, according to Harvard School of Public Health (HSPH) researchers. One of the most widely used industry standards, the Whole Grain Stamp, actually identified grain products that were higher in both sugars and calories than products without the Stamp. The researchers urge adoption of a consistent, evidence-based standard for labeling whole grain foods to help consumers and organizations make healthy choices. This is the first study to empirically evaluate the healthfulness of whole grain foods based on five commonly used industry and government definitions.

“Given the significant prevalence of refined grains, starches, and sugars in modern diets, identifying a unified criterion to identify higher quality carbohydrates is a key priority in public health,” said first author Rebecca Mozaffarian, project manager in the Department of Social and Behavioral Sciences at HSPH.

The Harvard researchers evaluated 545 grain products from two major grocery store chains, Stop & Shop and Walmart. They tallied up grams of whole grains in each product, along with the amounts of carbohydrates, fiber, added sugar, trans fat, and sodium, plus the number of calories. Foods that met the 10:1 ratio tended to have less sugar, sodium, and trans fats than those that didn’t.

“You aren’t alone if you are confused about whole-grain foods,” said Rebecca Mozaffarian, a project manager for the HSPH Prevention Research Center and first author of the study. She and her colleagues started this project when they realized there was little evidence-based information for guiding consumers, schools, and other organizations about choosing healthful whole grain foods.

Why bother eating whole grains? They deliver everything an intact grain has to offer—fiber, vitamins, minerals, antioxidants, and other phytochemicals. As long as they aren’t overprocessed, the body digests them more slowly, which can delay hunger. And large, long-term studies have shown that consuming whole grains is one way to help reduce the odds of developing heart disease, diabetes, and other chronic conditions. They also taste better than processed grains.

Intact grains—wheat berries, oat berries, brown rice, quinoa, and the like—are the best source of whole grains. “They’re a slam dunk,” says Mozaffarian. Ground whole grains come next, as long as they still deliver a good dose of fiber and don’t also deliver added sugar, trans fats, or sodium. To find those, I’ll be using the 10:1 carbohydrate-to-fiber guide.